Permeability-tuned wave trap and core construction therefor



March 25, 1941. J. g 2,236,292

PERMEABILITY-TUNED WAVE TRAP AND cons CONSTRUCTION THEREFOR Filed April 14, 1938 INVENT OR. MART/NJ k/EK.

ATTORNEY.

Patented Mar. 25, 1941 UNITED STATES PERMEABILITY-TUNED wave TRAP AND cons cons'rnoc'rron THEREFOR Martin J. Kirk, Chicago, 111., assignor to Johnson Laboratories, Inc., Chicago, 111., a corporation of Illinois Application April 14, 1938, Serial No. 201,915

8 Claims.

My invention includes a form of wave trap for use with radio receivers for connection with the antenna circuit, by which a selected frequency of carrier waves may be prevented from entering a radio receiver, either by by-passing the selected frequency around the receiver to ground, or by blocking the flow of current of the selected frequency in the antenna circuit of the receiver, so as not to interfere with the operation of the 10 receiver by currents of other frequencies. By my construction, the wave trap is provided with an inductance coil connected with a fixed condenser to form a resonant circuit, which resonant circuit is either connected between the antenna circuit and ground, or is serially included in the antenna circuit, as the case may be. The wind ings of the coil are so disposed and are of such number that in cooperation with the capacitance of the fixed condenser, a resonant condition is 20 produced in the resonant circuit at substantially the selected frequency, and I preferably tune the resonant circuit to exactly said frequency, by means of a core of comminuted magnetic material which is associated with the coil and mov- 25 able relative thereto to change its inductance to effect the accurate tuning referred to.

To eflectively operate the said core of the wave trap, I provide an improved connection and operating device for the core, comprising a connecting member of resilient material which is secured or rigidly attached to an operating rod and also secured to the said core, the resilient connector being if desired, of a material to insulate the operating rod from the core. To hold 35 the core'in place, and accurately maintain its inductive relation to the inductance coil, the coil is preferably wound on a tube of insulating material, in which tube the core is contained with a free sliding fit so that it may be moved axially o of the coil and so change, as desired, the inductance of the coil. The operating rod connected with the core is preferably threaded and engages a threaded member so that by turning the rod,

the core is moved axially of the coil. The resilient connection between the operating rod and the core, thus not only connects the core to the rod and if desired, insulates the core from the rod, but, in addition, it provides a connection of 50 a yielding nature such that if the threaded memmake the core tubular, and to connect the ,rod with the core I provide the resilient connecting member with an integral cylindrical extension larger in diameter at its base portion than the longitudinal hole in the core, so that the cylin- 5 drical extension which is preferably of reduced diameter at its outer end, may be drawn through the hole of the core and stretched in so doing, as a result 01' which, when the core is in proper position upon the connecting member, the cyllndrical extension of the connecting member is in a compressed condition in the hole of the core, which securely holds the connecting member and core together for the purposes contemplated. Whenthe core and connecting member are so connected, the projecting end of the cylindrical extension from'the connecting member is cut oil leaving a short portion protruding from the core.

This portion, being relieved of compression, expands to form a head which helps to retain the core on the connecting member, and the core and operating rod are yieldingly and effectively connected together. In practice, I find that rubber compound serves admirably as the material for the connecting member described, which compound may be molded around the end of the operating rod and vulcanized thereto if desired, the rubber compound being so selected as to have sufllcient resilience to constitute a yielding connection between the operating rod and the core and to be susceptible of suflicient reduction in diameter by stretching it, so that the extension from the connecting member will efiectively hold the core in place on the connecting member by the expansion tendency of the cylindrical extenslon when it is relieved from the stretching incident to mounting the core on the connecting member. I do not limit myself to using the core mounting construction described, with wave traps of the kind described; as the said core mounting and operating devices may be effectively used in any connection where it is desired to employ comminuted magnetic cores movable axially of inductance coils or windings to change the effective inductance thereof. i

My invention will be best understood by reierence to the accompanying drawing illustrating a preferred embodiment thereof, in which Fig. 1 shows in longitudinal, central, sectional view, an inductance coil and a movable core of comminuted magnetic material constituting the variable inductance element of my wave trap, together with connections schematically illustrating the remaining portions of one form of the wave trap and it manner of use,

Fig. 2 shows in side elevation and to an en-- larged scale, a threaded operating rod and resilient connecting member before a core has been mounted thereon to produce the movable core structure shown in Fig. 1, the connecting member shown in Fig. 2 being illustrated partially in vertical, central, sectional view to show the relation of the end of the operating rod thereto,

Fig. 3 shows in end elevation, the structure illustrated in Fig. 2,

Fig. 4 shows in central, longitudinal, sectional view a core of the kind illustrated in Fi 1, before it is mounted on the connection member shown' in Fig. 2.

Fig. 5 shows in a view similar to Fig. 2, the core illustrated in Fig. 4 mounted on the connection member illustrated in Fig. 2, the core being shown in central, vertical section in Fig. 5, and

Fig. 6 shows in schematic view, a'mo'dified form of wave trap.

Similar numerals refer to similar parts throughout the several views.

Asshown in Fig. 1, my wave trap consists of an inductance coil Ill having its windings wound on a tube II of insulating material, which tube is rigidly mounted at one end on a plug I2 having a central shouldered portion engaging a terminal strip I 3 of insulating material held on the plug by the tube II. The outer end of the shouldered portion of the plug I2 engages a mounting plate It through which said plug extends, the outer end of the plug being externally threaded to engage a nut I5 holding the inductance unit on the mounting plate I4. The tube II contains with a sliding fit, a core I6 of comminuted magnetic material, having an axial hole I6a containing the cylindrical extension Ila of a resilient connecting member Il formed around the head I8a of an operating rod I8, which operating rod is externally threaded and engages similar internal threads in the plug I2, the outer end of the rod being slotted at I 8b to facilitate turning the rod to adjust the core I6 axially of the coil III as desired.

The terminals of the coil I0 are connected by wires I9 and 20 with connection lugs 2I and 22 mounted on the terminal strip I3, which also carries a connection lug 24 connected with one terminal of a condenser 25 of fixed capacitance, the other terminal of which is connected with the lug 22. A series relation is thus established between the coil I0 and the condenser 25 which may be made resonant at the frequency it is desired to by-pass fromthe antenna circuit to ground.

In using the wave trap described to by-pass a selected frequency of carrier waves, oneterminal of the resonant circuit, for example, the lug 2i, is connected by a wire 23 with an antenna 28,

and the other terminal of said resonant circuit,

for example, the lug 24, is connected by a wire 21 with grounds as illustrated at 29, and the antenna connection with the wire 23 is also connected by a wire with the radio receiver, not shown. In many uses of radio receivers, due to particular conditions that may obtain in one 10- cality or another, it is important to protect the radio receivers from the undesired efiect of some selected frequency of carrier waves that may be particularly strong and undesirable in that locality. The wave trap construction described is effective in by-passing any said selected frequency of carrier waves, by accurately tuning the resonant circuit described to the selected frequency, which is done by making the coil III so that its efiective inductance cooperating with the capacitance of the fixed condenser 25 will establish a resonant condition in the circuit including said coil and condenser, at substantially the selected frequency it is desired to by-pass, and then when the wave trap is connected as described, adjusting the core I6 until the said resonant circuit is tuned exactly to the said selected frequency, for which condition a path of practically zero impedance is provided from the antenna 28 to ground for the selected frequency, as a result of which it does not reach the radio receiver through the wire 30, and doesnot interfere with the proper reception of carrier waves of other frequencies. In this way, the capacitance of the connecting wiring is compensated for, by tuning the wave trap to the selected frequency.

In Figs. 2 and 3, I illustrate the relation of the operating rod I8 and connecting member Il to each other before the core is mounted on the connecting member. As shown in these figures, the connecting member Il surrounds the head I8a of the rod I8, to which it may be secured either by cement of a suitable kind or by molding the material of the connecting member around said head in making said connecting member. I prefer to construct the connecting member ll of rubber compound having substantial resilience,

- so that in use, the connecting member may yield to accommodate irregularities of alignment of the nut engaging the threaded rod I8, and the tube containing the core mounted on the connecting member. The cylindrical extension Ila which is integral with the body portion of connecting member I7, is, in its original form, somewhat more than twice as long as the core, and

the outer portion of said extension is tapered as shown at Ilb, to freely enter the hole I 6a in the core I6, so that the end of the cylindrical extension may be engaged to stretch the cylindrical extension in placing the core on the connecting member with its end against the shoulder Ilc of said connecting member. The diameter of the cylindrical extension I la is somewhat larger than the diameter of the hole I6a in the core, and the stretching of the cylindrical extension sufllciently lustrated in Fig. 5, the core is securely held by the tendency of the cylindrical extension Ila to expand, when it is relieved from the stretching referred to. If desired, the extension Ila may also be cemented in the hole of the core I6, to further secure it thereto, although this is usually not necessary. When the core has been mounted reduces its diameter so that the core may be readily slipped on to the cylindrical extension Ila against the shoulder I 10, in which position, 11-

on the extension Ila as described, the projecting mounting tube I I, the outer diameter of the con- Il is preferably somewhat necting memb smaller than the outer diameter of core I6.

As a result of the construction described, I pro;

vide amounting means for magnetic cores which is cheap and efiective, and may be used wherever it is required to adjust such cores axially in inductance coils.

In the wave trap arrangement schematically illustrated in Fig. 6, the variable inductance coil I0 and condenser 25 of fixed capacitance, are connected in parallel, and the resonant circuit thus formed, is serially included in the antenna circuit of the receiver, by connecting one terminal of the resonant circuit with the antenna 28, and by connecting the other terminal of said resonant circuit with the wire 30 constituting the radio frequency input wire extending to the receiver. With this arrangement, when the resonant circuit is accurately tuned to the selected frequency, current of said frequency is prevented from flowing in the wire 30 and so reaching the receiver, y the high impedance of the resonant circuit at the selected frequency, without interfering with'current flow through the resonant circuit and to and through the wire 30 to the receiver, at frequencies other than the said selected frequency, within the reception band for which the receiver is constructed. The inductance coil I0 is preferably constructed, and its inductance is preferably varied in tuning the wave trap, in the same manner described above in connection with Fig. 1. 4

While I have shown my invention in the particular embodiment above described, it will be understood that I do not limit myself to the exact constructions described in carrying out my invention, as I may employ equivalents thereof without departing from the scope of the appended claims.

Having thus described my invention, what I claim is, v

1. Incombination, a tubular core of magnetic material, an operating rod spaced from said core, and a straightand non-metallic connecting member of fiexible'material secured to said. core and to said rod and extending in compressed condition into the hole in said core.

2. In combination, a tubular core of magnetic material, an operating rod spaced from said core, and a connecting member of resilient rubber compound secured to said core and to said rod and extending into the hole in said core.

3. In combination, a tubular core of magnetic material, an operating screw having a head spaced from said core, and a straight and non-metallic connecting member of resilient material around said head and extending in compressed condition into the hole in said core.

4. In combination, a tubular core of magnetic material, an operating screw having a head spaced from said core, and a connecting member of resilient rubber compound around said head and extending in compressed condition into the hole in said core.

5. In combination, a tubular and cylindrical core of magnetic material, an operating screw substantially coaxial with said core and having a head spaced therefrom, and a cylindrical and shouldered connecting member of resilient material around said head and extending in compressed condition into the hole in said core with its shoulder engaging the end of said core, said connecting member having an outer diameter smaller than the outer diameter of said core.

6. In combination, a tubular and cylindrical core of magnetic material, an operating Screw substantially coaxial with said core and having a head spaced therefrom, and a cylindrical and shouldered connecting member of resilient rubber compound around said head and extending in compressed condition into the hole in said core with its shoulder engaging the end of said core, said connecting member having an outer diameter smaller than the outer diameter of said core.

'7. A tuning unit for radio circuits comprising an insulating tube having an inductance coil disposed thereon, a ferromagnetic core for said coil, a rubber stem extending centrally through said core and fixedly secured thereto, said stem having an enlarged head portion at one of its ends, and a core-adjusting element forming an axial continuation of said stem, having an end portion firmly embedded in the enlarged end portion thereof.

8. A tuning unit for radio circuits comprising in combination, a tubular member having an inductance coil disposed thereon, a cylindrical core of magnetic material for said coil, an operating screw substan'tially coaxial with said core and having a head spaced therefrom, and a cylindrical and shouldered connecting member of resilient material around said head and extending in compressed condition into a hole in said core with its shoulder engaging the end of said core, said connecting member having an outer diameter smaller than the outer diameter of said core.

MARTIN J. KIRK. 

